1. Field of the Invention
The present invention relates generally to aluminum melting furnaces, and particularly to an installation for feeding cells of aluminum melting furnaces with bulk material such as pulverized aluminum oxides.
2. Technical Background
In one approach that has been considered, an installation includes an aluminum oxide storage bunker is connected with a pneumatic (air fluidizing) conveying chute. The conveying chute comprises a multiplicity of lateral discharges, each of the lateral discharges being connected with a pneumatic conveying chute. Each chute includes separate discharges for the individual cells of the aluminum melt furnace.
In another approach that has been considered, an installation for feeding bulk material containers includes a pneumatic conveying line that is connected with the containers by way of a valve arrangement. The valve arrangement is such that each valve closes automatically when the fill level in the container reaches a predetermined value. One drawback to the aforementioned approaches relates to the high energy consumption involved in supplying large furnaces that include a multiplicity of cells.
What is needed is an installation for feeding an aluminum melt furnace having a plurality of loads (e.g. cells), with pulverized aluminum oxide. It is desirable that the installation be equipped to supply of a large number of cells while consuming a relatively low amount of energy.
The present invention addresses the above described needs. The present invention provides an installation that is capable of feeding pulverized aluminum oxide to an aluminum melt furnace having a plurality of cells. The installation of the present invention is equipped to supply of a large number of cells while consuming a relatively low amount of energy.
One aspect of the present invention is an Installation for feeding a plurality of cells of aluminum melting furnaces with bulk material, such as pulverized aluminum oxide. The installation includes a silo for storing aluminum oxide. The silo is connected with a pressure vessel or pump delivering machinery, which on its part feeds a pneumatic conveying line (or air conveyer). Pressure vessel or pump delivering machineries are used to convey bulk material for long distances while consuming relatively low amounts of energy. It is therefore possible to deliver the aluminum oxide material to a plurality of acceptance sites disposed at different locations. According to the invention, so-called receiving or intermediate vessels are coupled to the conveying lines in the vicinity of the aluminum melt furnace. The receiving vessels are connected to the conveying line via valves. Each receiving vessel itself is connected with the cells of the aluminum melt furnace by at least one pneumatic conveying chute. The pneumatic conveying chute includes a discharge mechanism for each cell of the furnace.
A pneumatic conveying chute for conveying bulk material has the considerable advantage that a pressure-tight sealing of the furnace cells is not required. Upon using a pneumatic conveying line at this point, a pressure-tight sealing is indispensable, because otherwise considerable amounts of dust would leak out of the furnace cells and would contaminate the area surrounding the furnace.
It is understood that above and below the conveying chute, a tube may be employed that includes a separate channel in its downward region that can be flushed with air. In upward direction the tube is permeable, such that the desired fluidization of the conveyed bulk material is achieved.
When rigidly connecting the conveying chute with the receiving vessel and the corresponding entry to the cells of the aluminum melt furnace, the risk exists that an adjustment of the conveying chutes in longitudinal direction is required because of the structural arrangements. Therefore another embodiment of the invention provides that the conveying chutes have a first chute segment connected with the receiver vessel, and a second segment which is connected with the lateral discharge and which co-operates with the first chute segment in a telescopic manner. Thus a spatial adaptation of the conveying chutes is realized. Furthermore it is possible to change the position of the receiving vessel without having to change the junctions on the aluminum melt furnace and the conveying chutes, respectively.
The second segment co-operating in a telescopically manner with the first chute segment can also be constructed as a pneumatic conveying line by providing it with a sieve-shaped aerating plate and connecting it to a compressed air source. Thus it is guaranteed that a problem-free conveying of the bulk material up to the discharge, e.g. to the aluminum melt furnace, is secured.
The fill-up valve between the pneumatic conveying line and the receiving vessel is controllable. It must naturally be prevented that the receiving vessel is congested and causes a jam in the conveying line under certain circumstances. According to the invention, a controlling means for actuating the valve is therefore provided, and the controlling means responds to a fill level indicator device, which detects when the level in the receiving vessel reaches a predetermined upper value.
It is conceivable to provide for a second fill level indicator in the receiving vessel, which responds when the receiver is approaching the state of emptiness. In this case, the valve is then opened again. During the operation of the aluminum melt furnaces, e.g. aluminum oxide is discontinuously conveyed through the pneumatic conveying line. As the consumption per time unit is known, the delivery per time unit can be accommodated to this consumption. This also holds for the receiver vessel, so that a fill level measurement for the downward level may also be omitted. If appropriate, the valve can be controlled in a time-dependent manner, namely, it can be opened after a certain time after closing, this time corresponding to that one which is required for each cell of the furnace to be continuously fed from the receiving vessel.
According to a further embodiment of the invention two or more pneumatic conveying chutes per receiving vessel are provided, preferentially on opposing sides, each leading to a load arrangement, e.g. an aluminum melt furnace with a plurality of electrolytic cells.
According to another embodiment of the invention a monitoring and indicating device is provided for the valves. It determines whether the valve is actually closed, after a corresponding actuation signal for adjustment into the closing position has been transmitted to the valve from the fill level indicator and the controlling means, respectively. It has also to be determined whether the valve has been adjusted into the opening position after a fresh refilling of the receiving vessel has become necessary.
A conventional feed valve for such pneumatic conveying systems may be employed as the valve. According to one embodiment of the invention the valve is provided to be a valve ball with an axial passage as the valve member, mounted rotationally in a valve body. An elastic sealing ring is disposed on the side of the valve ball facing the conveying line and co-operates with the valve ball. On the opposite side of the valve ball, sufficient distance to the valve body is provided. To actuate the valve ball, e.g. a pneumatic actuation unit is used with which the valve ball is deviated to an angle of 90xc2x0 from the opening position into the closing position and vice versa. The internal pressure in the receiving vessel is lower than in the pneumatic conveying line operating at overpressure. In the closed position of the valve a pressure difference at the sealing ring is consequently generated, so that the latter is inevitably pressed against the ball surface. The sealing action increases with increasing pressure difference.
The valve ball is sealed only unilaterally, on the side of the higher pressure. On the side of lower pressure no sealing exists, the body featuring a large spacing towards the ball instead. In this way the forces required to open and close the valve are reduced to a minimum. Furthermore, no deposition of bulk material can occur upon perpendicular incorporation of the feed valve, especially in the opened position. This increases the operational safety of the valve, because the forces required to actuate the valve remain calculable.
According to a further embodiment of the invention the conveying line is provided to be connected at opposing sides of a cylindrical body open-ended in the downward direction, and the valve body is provided to be disposed at the bottom end of the cylindrical body in a sealed manner.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.